Learning Set 1 • How Do Flowing Water and Land Interact in a Community?
1.8 Read
What are Some Sources of
Pollution in a River?
pollution:
substances added
to air, water, or
soil that cause
harm to the
environment.
You built and ran models of land use using a stream table. You observed the
effects of the different kinds of land use on erosion, deposition, and runoff
in a watershed. During the classroom discussion, you might have discovered
something more. Human activities also change the quality of the water.
As the water flows through the watershed, it carries with it stuff it picks up
along the way. This could be dirt and soil eroded from land. Runoff and
groundwater can also pick up substances like chemicals, small particles, and
pieces of trash that can affect the quality of the water. Scientists call these
substances that end up in the river pollution. Pollution can cause harm
to human health or the environment. Most of the time, these substances
result from human activities. Normally, they are not found in natural
environments. They can be very dangerous because living organisms may
not be able to handle them.
Stop and Think
Look at the pictures below and on the next page. You might have seen
scenes like these in your neighborhood, or town. People are walking down
the street. People are washing their cars. Some are taking care of their
lawns. Someone is pouring something down a sewer drain. Workers are
fixing something under the street.
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1.8 Read
Answer the following questions as you look at the pictures.
1. What kind of land use does each picture represent?
2. Identify all of the examples of human activities shown in each picture.
Describe how each activity might cause pollution.
3. How might each land use affect the local runoff and groundwater?
4. Think about what might happen in each place when it rains. Describe
what could be on the ground that might cause pollution in a river.
Sources of Pollution in Rivers
Once pollutants get into soil or water, they are carried by surface and
groundwater to rivers. In this way, they are distributed over large areas,
sometimes miles away from their source.
Depending on how the pollution enters a body of water, pollution sources
are divided into two groups: point-source pollution and non-pointsource pollution.
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point-source
pollution:
pollution that
originates from
a single point or
location.
non-pointsource
pollution:
pollution that
comes from
many sources
over a large area.
LIVING TOGETHER
Learning Set 1 • How Do Flowing Water and Land Interact in a Community?
Point Sources of Pollution
Point-source pollution comes from a specific point or location. From this
location, the pollution is discharged directly into rivers, lakes, or oceans.
Scientists can easily identify the source of this type of pollution. They
analyze the water at different points in the river or lake. The closer to the
point source they measure, the higher the amount of pollutant they find.
Examples of Point Sources of Pollution
Sources
leaking pipes
barrels leaking chemicals
smokestacks
sewage discharge
How the Pollution Enters the River
Pipes that transport oil or chemicals can release these
substances through cracks. These substances are carried
to rivers by water.
Old barrels containing chemicals are sometimes dumped
or buried in the ground. Over time, the chemicals leak
out of the barrels and are carried to the river by water.
Smokestacks from factories can release dangerous
chemicals into the air. When these chemicals fall to
the ground as small particles, or mix with rain,
they are carried to rivers by water.
Raw sewage, or sewage that is treated only partially,
sometimes is discharged directly into rivers. This sewage
can contain harmful chemicals and bacteria.
Non-Point Sources of Pollution
Non-point-source pollution comes from many sources and locations.
Scientists cannot easily identify all the sources of this pollution. For
example, one non-point source of pollution is runoff containing fertilizer
used on lawns or farmland. Because the runoff has material from so many
different farms or lawns, it would be difficult to pinpoint the source of the
fertilizer. Another non-point source of pollution is urban runoff from roads
and parking lots. Water running off these surfaces can carry oil leaked from
cars or salt used to melt ice to a river. This type of pollution is often carried
to the river by runoff over large areas. Non-point sources of pollution are
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1.8 Read
much more difficult to control. It is hard to determine who or what is
responsible for this pollution. Non-point sources of pollution can originate
from a very large land area such as an entire watershed.
Examples of Non-Point Sources of Pollution
Sources
fertilizer
urban runoff
litter
salt and sand
How the Pollution Enters the River
Many people fertilize crops, lawns, and other plantings.
Eventually, the fertilizer can be carried to rivers in runoff.
Vehicles and other equipment can leak lubricants
and fuel that eventually wash into rivers.
People drop or dump trash and litter in public spaces.
This litter is eventually carried to waters by wind
and runoff.
Communities spread salt and sand to prevent roads
from icing over. This eventually is carried to rivers
by runoff.
Reflect
Look back at the photographs you reviewed early in the Unit. The
photographs show scenes of the land use you were assigned and that you
modeled with your stream table. Discuss with your group the types of
pollution that may result from your land use.
• Record all of the pollution sources your group identifies in the photos,
including both point sources and non-point sources.
• Record any pollution sources you think might be there because of
certain activities or events shown in the photos.
• For each pollution example you record, determine if it is a point
source or non-point source of pollution. Make sure you write the
reason why you think so.
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LIVING TOGETHER
Learning Set 1 • How Do Flowing Water and Land Interact in a Community?
Your teacher will lead a class discussion where each group shares their
photos and their work. Listen carefully as other members of your group
discuss their observations and conclusions. With your class, review
and discuss the observations and conclusions drawn by other groups
investigating a different land use. How are the pollution sources similar or
different for each land use? Come up with a list of types of pollution you
agree upon. List the types of pollution you found for each of the land uses
your class has investigated.
Update the Project Board
The questions you focused on in this Learning Set were How does water
affect the land as it moves through the community? and How does
land use affect water as it moves through a community? Return to the
Project Board to update any questions or ideas you have posted. You now
have many items to post in the What are we learning? column. Be sure to
cite (in the What is our evidence? column) the evidence you collected to
support what you now know about pollution and land use. Discuss with your
class what you recorded on the Project Board that can help you answer
the two questions. You might make up and discuss several new ideas or
understandings that should be recorded on the Project Board.
What’s the Point?
There are many different ways that land use can add pollutants to a
watershed. All of the different ways of polluting are grouped into two different
types: point sources and non-point sources of pollution. Point sources of
pollution, the kind that happen in many industrial areas, are very harmful.
However, they are a lot easier to stop than non-point sources of pollution.
Non-point sources of pollution can be more difficult to find. They do not
come from a specific place. Agricultural areas and residential areas create a
lot of non-point sources of pollution through fertilizers.
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